The invention relates to a disc-type insulator with a cast-in electrode, which is designed to be used in enclosed high-voltage equipment. The cast-in electrode, which is convex-cambered towards the disc axis, extends along at least a portion of the periphery of the disc-type insulator, and is connected to contact electrodes which are located on the surface of the disc-type insulator, the connection being capable of conducting electricity.
Disc-type insulators are employed to retain a conductor, or a plurality of conductors, in the gas-filled interior of the enclosure, and, customarily, also for hermetically sealing of various portions of the enclosure. The cast-in electrode, which is connected to the enclosure via the contact electrodes in a manner such that electricity can be conducted, functions to prevent the occurrence of intense electrical fields at the anchorage point of the disc-type insulator in the enclosure. Corona discharges, which are otherwise impossible to prevent at a reasonable cost, which occur because of the unavoidable contact between conducting material and non-conducting materials possessing different dielectric constants (enclosure, disc-type insulator, insulating gas) are avoided by smoothing out the electric fields.
A disc-type insulator is described in U.S. Pat. No. 3,652,778. This disc-type insulator possesses a cast-in electrode which is designed as a continuous ring and which is connected to contact electrodes, by means of straight contact tongues, in a manner such that the connection conducts electricity. These contact electrodes serve at the same time as cast-in sleeves which carry threads.
In the case of a disc-type insulator, particularly one having a comparatively large diameter, it has been found that cast-in electrodes of the abovementioned design can easily be damaged and, in particular, distorted as a result of the shrinkage which occurs during the curing of the the disc-type insulating material after it has been cast, or as a result of thermal stressing during operation. Moreover, the contact tongues can be torn away, which can lead to the cast-in electrode becoming functionally unserviceable and, in consequence, to corona discharges and even to insulation breakdowns, or the insulator can break away from the cast-in electrode over a portion of the periphery.